Presentations

Abstract

The ability to use linguistic representations to refer to the world is a vital mechanism that gives human language its communicative power. In particular, the anaphoric use of words to refer to previously mentioned concepts (antecedents) is what allows dialogue to be coherent and meaningful. Psycholinguistic theory posits that anaphor comprehension involves reactivating an episodic memory representation of the antecedent [1-2]. Whereas this implies the involvement of memory structures, the neural processes for reference resolution are largely unknown. Here, we report time-frequency analysis of four EEG experiments [3-6], revealing the increased coupling of functional neural systems associated with coherent referring expressions compared to referentially ambiguous expressions. We performed time-frequency analysis on data from four experiments in which referentially ambiguous expressions elicited a sustained negativity in the ERP waveform compared to coherent expressions. In Experiment 1, 32 participants read 120 correct Dutch sentences with coherent or ambiguous pronouns. In Experiment 2, 31 participants listened to 90 naturally spoken Dutch mini-stories containing coherent or ambiguous NP anaphora. In Experiment 3, 22 participants each read 60 Spanish sentences with a coherent or ambiguous ellipsis determiner. In Experiment 4, 19 participants each read 180 grammatically correct English sentences containing coherent or ambiguous pronouns. Analysis was performed with Fieldtrip [7], separately for low frequency (2-30 Hz) and high frequency (25-90 Hz) activity. Power-changes per trial were computed as a relative change from a pre-CW baseline interval, average power changes were computed per subject for coherent and ambiguous conditions separately. Statistical tests used cluster-based random permutation [8]. Despite varying in modality, language and type of expression, all experiments showed larger gamma-band power around 80 Hz for coherence compared to ambiguity, within a similar time range. No differences were observed in low frequencies. In high-density EEG Experiment 4, an additional short-duration gamma-increase was observed around 40 Hz, around 300-500 ms after pronoun-onset, which was localised using Beamformer analysis [9] to left posterior parietal cortex (PPC). The 80 Hz power increase around 600-1200 ms after word onset was localised to left inferior frontal-temporal cortex. We argue that the observed gamma-band power increases reflect successful referential binding and resolution, linking incoming information to previously encountered concepts and integrates that information into the unfolding discourse representation. Specifically, we argue that this involves antecedent reactivation in the PPC episodic memory network [10-11], interacting with unification processes in the frontal-temporal language network [12]. Based on these results, and on results of patient [13] and fMRI [14] research on pronoun comprehension, we propose an initial neurobiological account of reference, by bridging the psycholinguistics of anaphora with the neurobiology of language and of episodic memory. [1] Dell et al., 1983 [2] Gerrig & McKoon, 1998 [3] Nieuwland & Van Berkum, 2006 [4] Nieuwland et al., 2007a [5] Martin et al., 2012 [6] Nieuwland, 2014 [7] Oostenveld et al., 2011 [8] Maris & Oostenveld, 2007 [9] Gross et al., 2001 [10] Shannon & Buckner, 2004 [11] Wager et al., 2005 [12] Hagoort & Indefrey, 2014 [13] Kurczek et al., 2013 [14] Nieuwland et al., 2007b

Abstract

The ability to use words to refer to the world is a vital mechanism that gives human language its communicative power. In particular, the use of words to refer to previously mentioned concepts (anaphora) is what allows dialogue to be coherent and meaningful. Psycholinguistic theory posits that anaphor comprehension involves reactivating a memory representation of the antecedent. Whereas this implies the involvement of episodic memory, the neural processes for reference resolution are largely unknown. Here, we report time-frequency analysis of four EEG experiments to reveal the increased coupling of functional neural systems associated with referring expressions that can be straightforwardly understood compared to those that cannot (referential coherence or ambiguity). Despite varying in modality, language and type of referential expression, all experiments showed larger gamma-band power for coherence compared to ambiguity. In high-density EEG Experiment 4, Beamformer analysis localised this increase to the posterior parietal cortex around 300-500 ms after onset of the anaphor and to frontal-temporal cortex around 500-1000 ms. We argue that the observed gamma-band power increases reflect successful referential binding and resolution, which links incoming information to previously encountered concepts through an interaction between the episodic memory network and the frontal-temporal language network.

Abstract

In general, language comprehension is surprisingly reliable. Listeners very rapidly extract meaning from the unfolding speech signal, on a word-by-word basis, and usually successfully. Research on ‘semantic illusions’ however suggests that under certain conditions, people fail to notice that the linguistic input simply doesn’t make sense. In the current event-related brain potentials (ERP) study we examined whether listeners would spontaneously detect an anomaly in which a human character central to the story at hand (e.g. “a tourist”) was suddenly replaced by an inanimate object (e.g. “a suitcase”). Because this replacement introduced a very powerful coherence break, we expected listeners to immediately notice the anomaly and generate the standard ERP effect associated with incoherent language, the N400 effect. However, instead of the standard N400 effect, anomalous words elicited a differential ERP effect from about 500-700 ms onwards. The absence of an N400 effect indicates that subjects did not immediately notice the anomaly, and that for a few hundred milliseconds the comprehension system has converged on an apparently coherent but factually incorrect interpretation. The presence of the later ERP effect indicates that subjects were processing for comprehension and did ultimately detect the anomaly. Therefore, we take our results to reflect a temporary semantic illusion. Our results also show that even attentive listeners sometimes fail to notice a radical change in the nature of a story character, and therefore demonstrate a case of short-lived ‘change deafness’ in language comprehension.

Abstract

n two ERP-experiments we examined whether discourse context could overrule a local semantic violation. In both experiments, subjects listened to stories in which a person was engaged in conversation with an inanimate object. In experiment 1, story-initial animacy violations reflected in an N400 effect were completely neutralized further down the story. In experiment 2, canonical but story-irrelevant inanimate predicates assigned to the inanimate object elicited an N400 effect, compared to contextually appropriate animate predicates.